As a company that cares for the environment, we strive to reduce or eliminate air emissions of environmentally harmful substances. This is a tremendous challenge given the company's fast-growing service territory, and increased per capita electricity consumption, which requires us to continue adding generation assets to meet this demand. 

Our company maintains air emissions per megawatt-hour at or below industry averages. This is achieved through the use of nuclear power, emissions control technology, improved power plant efficiency and a more diverse fuel mix which includes nuclear, gas/oil, coal and renewables. In addition, we have an aggressive demand side management program that works to improve energy efficiency and reduce per capita demand.

In 2005, APS purchased 51.8 percent of its power from external sources, and generated 48.2 percent of its power internally. Our 2005 generating capacity is shown below:

Note that the emissions of these pollutants per megawatt hour continues to drop in 2005, reflecting our continued efforts to generate electricity with lower air emissions per unit generated (i.e. a lower intensity factor). Also, emission of sulfur dioxide showed a significant reduction in 2005 in both total tons emitted and tons per megawatt hour. This was due to our continued voluntary efforts at Four Corners and Cholla power plants to reduce air emissions (see below). 

The emissions chart for Volatile Organic Compounds (VOCs) shows a drop in 2005. This was due to a change in the emission factor we are using for reporting Four Corners Power Plant VOC emissions. Previously, we used  the generic AP-42 VOC emissions factor to calculate total VOC emissions. In 2005, we started using a more accurate method (EPRI Emissions factors), which calculates the emissions for each individual VOC and then sums the total. This method is consistent with the plants Title V air permit, and we believe it is a more accurate calculation of the actual emissions.

Planned Voluntary Emission Controls at Cholla and Four Corners Coal-fired Plants

In the late 1990s, APS initiated a dialog with four environmental interest groups involved in environmental issues in the western United States: Environmental Defense, the Grand Canyon Trust, Western Resource Advocates and the New Mexico Citizens for Clean Air and Water.

The discussion centered on the complexities of environmental laws confronting the electric utility industry and on ways to navigate that complexity without the historic confrontation that exists between the industry and environmental groups.

The dialogue focused on the issue of visibility in the western United States. The Clean Air Act designates 156 large national parks and wilderness areas as “Class I areas” and provides for protecting visibility in those areas. The Environmental Protection Agency’s (EPA) visibility regulations require specific emissions limitations on sources causing, or contributing to, visibility impairment in Class I areas. Those rules focus primarily on sulfur dioxide emissions, and to a lesser extent on NOx and PM emissions, from large stationary sources such as coal-fired power plants. All three of APS-owned coal-fired power plants are located on the Colorado Plateau which contains numerous Class I areas.

Four Corners Power Plant
In 2003, APS and these environmental groups agreed on a proposal geared to further reduce sulfur dioxide emissions at the Four Corners plant utilizing an 18-month test program. The test program involved certain phased operational changes and scrubber chemical process changes to increase sulfur dioxide control levels from 72 percent to 85 percent, without triggering operational problems or incurring significant new capital expenditures. APS and the environmental groups jointly presented that proposal to the EPA, NEPA and the National Park Service (NPS). With the enthusiastic support of these groups, APS initiated the test program in early 2004.

The test program was completed during the summer of 2005. APS prepared a report concluding that the plant not only was able to meet the goal set in the proposal, but it also improved sulfur dioxide controls to an 88 percent level. At that elevated control level, the plant was able to cut its annual sulfur dioxide emissions by more than 55 percent, compared to the pre-test level. APS and these environmental groups are working with the EPA, NEPA, and NPS to incorporate the higher sulfur dioxide control level as an enforceable emission limit for the plant.

The dialog with these environmental groups also dealt with NOx emissions. Both sides agreed that potential future emission reductions will come from combustion-modification approaches rather than through the use of post-combustion techniques, such as Selective Catalytic Reduction (SCR). Jointly, APS hired an independent consultant charged with assessing the potential for reducing the plant’s NOx emissions, by adding "over-fire-air" to exiting low NOx burners.   The consultant’s report concluded there was little room for improving combustion controls at the three smaller units, although further detailed evaluations were needed to assess potential combustion controls for the two larger units. APS is studying such control options and continues its dialog with the environmental groups.

Cholla Generating Station
The dialog between APS and the environmental groups also resulted in an agreement in 2005 relating to several pollution-control enhancements at the Cholla plant. ADEQ and the EPA also were involved in the year-long discussions on selecting the extent and schedule for the planned pollution-control upgrades. Based on this agreement, APS filed an application with ADEQ to revise the plant’s Clean Air Act (CAA) Title V Operating Permit to include these pollution control projects.  We will report on the results of this effort in our 2006 report.

Emissions technology mix
APS has a total of about 1,100 MW of generation capacity (all coal) which is scrubbed with Venturi scrubbers, flooded disc scrubbers or absorbers. APS has about 1,500 MW of generation capacity with SCR (all natural gas). APS has another 1,300 MW of generation capacity with low NOx burners.